This invention relates to machines for making filled packages, and deals more particularly with package making machines of the type wherein a tube of packaging material is sealed periodically along longitudinally spaced lines extending transversely of the tube and is supplied with charges of product introduced to the tube between successive transverse seal formations.
The control system of this invention is herein shown and described, by way of example, in association with a package making machine of the type commonly referred to as a vertical form, fill and seal machine wherein the tube is made in the machine by folding a web of packaging material and sealing its overlapped side edges. However, at least in its broader aspects, the invention is not necessarily limited to such application and may find utility in other types of packaging machines, such as those in which the tube of packaging material is preformed apart from the packaging machine or formed by the packaging machine in some other manner. Hereinafter in this description, and in the claims which follow, the term "bag" is usually used to refer to the container produced by the machine in question and as so used it is intended to be generally synonymous with other terms such as "package", "pouch" or "envelope" which might have been equally as well chosen for the purpose.
In packaging machines of the transversely sealed tube kind, it is often desirable to have the capability of varying the length of the bags produced to suit the weight or volume of product to be contained in each bag, or to correspond to the length of each repeat of matter printed on the tube. Accordingly, it has been common to provide for some bag length adjustment, but usually the adjustment has been difficult to make and often requires shifting or replacement of timing cams or other mechanical parts which is time consuming; and, often the adjustment can be performed only while the machine is stopped. Further, the bag length determining mechanism is often interrelated with the sealing mechanism in such a way that adjustment of bag length disturbs the timing of the sealing function and thereby makes necessary some adjustment of the sealing mechanism to bring the machine back to a condition of proper operation at the new bag length.
Also, in packaging machines of the type with which this invention is concerned, it has been common in the past to feed the tube of packaging material through the machine by a reciprocating end sealer, the jaws of the sealer serving not only to form transverse end seals in the tube but also serving to grip and pull the tube through the machine as the end sealer moves in one direction of its reciprocating motion. Thus, in these machines the tube feeding function and the end sealing function are performed during the same portion of each bag making cycle, and the amount of time devoted to tube feeding during each cycle cannot be shortened beyond the minimum amount of time required to produce satisfactory end seals. If, in such machines, the tube is made by folding a web of sheet material into a tube with overlapped longitudinally extending side edges, and sealing the overlapped side edges to one another by a longitudinal seam sealer, the longitudinal seal forming operation is commonly performed during the return stroke of the end sealer when the tube is stationary relative to the remainder of the machine. Thus, the end seal operation and the longitudinal seal operation occur in different portions of the bag making cycle and each requires an associated minimum amount of time to effect acceptable seals. That is, each bag making cycle must include a first minimum amount of time for making satisfactory end seals and a second minimum amount of time for making a satisfactory longitudinal seal, and each cycle cannot be shortened in time beyond the sum of such two minimum time periods.
The general object of this invention, therefore, is to provide a control system for a vertical form, fill and seal packaging machine, or other packaging machine of the transverse tube sealing kind, having the capability of bag length adjustment by means of nothing more than a manually rotatable knob or similar easily manipulatable control element.
A further object of the invention is to provide a bag length adjusting means such as aforesaid whereby the bag length may be adjusted while the machine is running so as to allow the effect of a given change in the adjustment to be immediately observed.
Another object of the invention is to provide a bag length control means for a packaging machine such as aforesaid whereby changes in the bag length and machine speed (bags per minute) may be varied, without tools, while the machine is running and without causing problems in the sequencing of the tube feeding and sealing functions. In keeping with this object of the invention, the tube feeding function and the sealing function (that is, the end sealing function and the longitudinal sealing function, if any) are separated from one another so as to occur during different portions of each bag making cycle, but the sealing function is timewise interlocked to the tube feeding function so that, in each bag making cycle, the sealing function is initiated immediately upon the ending of the tube feeding function regardless of the length of time devoted to the tube feeding function. Therefore, changes in the tube feed time per bag making cycle and changes in the speed of the machine may be made without resulting in timewise overlaps in or gaps between the tube feeding and sealing functions.
Another object of the invention is to provide a packaging machine control system of the foregoing character whereby the machine is or may be operated on a product demand basis -- that is, on the basis of a bag being made only in response to operation of the product feeder to deliver a product charge to the tube, thereby effecting a "no product -- no bag" result.
Other objects and advantages of the invention will be apparent from the drawings forming a part hereof and from the following detailed description and claims.